1. Field of the invention:
The present invention relates to a method of and an apparatus for evaluating the performance of a dielectric fluidic substance such as lubricating oil, cutting oil, coolant oil, and the like.
2. Description of the Prior Art:
Generally, dielectric substances such as oil and grease gradually vary in performance in its process of use or with time. Lubricating oil, as an example of such a substance, is employed as a lubricant for mechanical frictional members in engines, in automobiles and ships and industrial machines such as machine tools and textile machines. The lubricating performance of the lubricating oil gradually decreases due to entrapment of metal particulates in the oil in the process of use or oxidization and property changes of the oil itself.
The lubricating oil used in internal combustion engines particularly suffers from a large reduction of performance as it is used. Therefore, it is necessary to periodically inspect the lubricating oil and replace it, if its performance is lowered, with new lubricating oil for maintaining required characteristics of the internal combustion engine.
Several processes have been employed for recognizing or grasping deterioration of lubricating oil. One known such process is a quantative analysis of a viscosity reduction, an oxidation degree, an increase of residual carbon, an increase of insolubles, and the like. Another conventional process is electrically effected for measuring the above variables as variations in the dielectric constant or conductivity.
For the quantative analysis of the variables, it is necessary to sample the lubricating oil from an internal combustion engine and subject the oil to a chemical analysis. This procedure is quite time-consuming, requires expensive and complex measuring equipment, and hence is not practical.
The method of recognizing the performance of lubricating oil based on a variation in its dielectric constant and conductivity is relatively simple. However, the oil performance cannot accurately be determined simply on the basis of the sole information of dielectric constant or conductivity.
More specifically, lubricating oils for use in internal combustion engines vary in initial performance dependent on the kinds of additives contained therein, and their dielectric constants and conductivities differ widely. The manner in which the oil performance is lowered varies with the condition in which the engine operates. Therefore, the latter method is disadvantageous in that the dielectric constant or conductivity as measured may not be a direct indication of the performance of the lubricating oil itself.
Still another evaluation process which has conventionally been carried out in general for lubricating oils for automobiles is an organoleptic test which is normally conducted by checking the running distance of an automobile or inspecting the color of the oil or its feel (through examination of the viscosity and insolubles on finger tips). The organoleptic examination however is not related to the oil performance and not a sensible method to resort to. This method does not allow the essential performance of lubricating oil to be recognized, and oil replacement is indicated only by indirect information such as the running distance or oil contamination. Therefore, the organoleptic method sometimes results in a wasteful consumption of lubricating oil, and is disadvantageous from the standpoint of saving resources.